Dyslexia affects the lives of millions of people world-wide and often has devastating psychological, social and educational consequences. It is also one of the most controversial topics in the fields of developmental neurology, psychology, and education. The controversy arises from the incomplete definition of the syndrome of dyslexia and from contradictory theories that surround its etiology.
A major difference between dyslexia and other reading disabilities is that, unlike dyslexia, other categories of reading failure can be predicted on the basis of neurological, intelligence, socio-economic, educational and psychological (motivational, emotional) factors known to adversely affect the reading process. If, for instance, a child has problems in one or more of the above-mentioned areas, he is expected to have reading problems. The extent of the reading disability is determined by the severity and number of factors that are involved.
In contrast, if a child has none of the above-mentioned problems, he is expected to be a normal reader. Children are presently classified as dyslexic when their failure to learn to read cannot be predicted by deficiencies in any of the known causes of poor reading. Psychological, socio-environmental, educational and intelligence factors do not cause dyslexia, although they can contribute to its severity or amelioration. The causes of dyslexia are unknown, and there is substantial disagreement on the definition of dyslexia. Lack of knowledge as to the causes of dyslexia has forced the adoption of definitions based on exclusionary criteria. The diagnosis of dyslexia by the use of exclusionary criteria delays diagnoses by at least 1.5 to 2 years after the beginning of school. This generally results in the development of psychological problems secondary to reading failure, and limited effectiveness of treatment following delayed diagnosis. Furthermore, children presently cannot be unequivocally diagnosed as dyslexics if they are:
(a) psychologically maladjusted prior to beginning schooling;
(b) from a disadvantaged socio-cultural background;
(c) educationally deprived; or
(d) of low intelligence.
It is thus desirable to develop a definition that would identify dyslexics on the basis of positive behavioral, psychological and/or neurophysiological symptoms such as abnormal EEG or evoked potential and/or erratic eye movements. A major advantage of a positive definition of dyslexia is that it would make possible an unequivocal diagnosis in children from disadvantaged socio-cultural and educational backgrounds, as well as in children who are psychologically disturbed or of low intelligence.
Applicant first noted a relationship between erratic eye movements and dyslexia at the University of Manchester, in England. The first known publication of this work was in the Manchester Evening News on Apr. 19, 1978. This article disclosed testing stimulus using a series of lights that flashed from left to right, an eye movement detector and a special video monitor which provided blips which indicated exactly where the subject was looking. According to this article, "It has simply turned out that dyslexics are unable to follow the lights properly *** whereas the control group of normal readers coped without difficulty."
Applicant authored an article entitled "How to Catch His Eye", while at the University of Manchester, that was published in Nursing Mirror, on Jan. 31, 1980, Vol. 150, p. 24-27. This article focused on various types of known eye movement detectors, their advantages and disadvantages. This article surveyed direct photographic recording, corneal reflection, contact lenses with mirrors or embedded coils of wire, photo-electric methods detecting the difference in reflectance between the dark iris and the white sclera of the eye and electro-oculography. This article did not apply the reviewed eye movement detectors to a dyslexia device, although it does set forth several desirable criteria that are necessary before an eye movement detector can be used in an apparatus for detecting dyslexia.
Applicant has also edited a book entitled Dyslexia Research and its Applications to Education and authored one chapter "Sequencing, Eye Movements and the Early Objective Diagnosis of Dyslexia". This book was published in England by John Wiley and Sons, Ltd. in October of 1981. This chapter does not disclose any specific device or method for analyzing eye movement, but does treat extensively the difference in eye movement patterns between dyslexics and normal or slow readers. The chapter does disclose a sequentially flashing LED display which was used as a visual stimulus for the tests.
U.S. Pat. No. 3,583,794 discloses a direct reading eye movement monitor that uses a pair of photo cells to monitor eye movement, and records the output signal from the eye movement detector on a moving strip chart to provide a graphic representation of the movement of the eyes of the subject.
U.S. Pat. No. 3,679,295 discloses an automatic electronic reading pattern analyzer that uses photo-electric eye movement monitors, and a circuit for analyzing the output of the monitors to provide the analyzed data in readable alpha numeric form. This patent describes an electrical device for distinguishing between normal advancements, fixations, and regressions and return sweeps which it terms the primary or characteristic eye motions of reading. The device, however, does not distinguish between saccade and pursuit movements, and it would appear that its sampling rate is not sufficiently fast to enable it to distinguish between a pursuit and a saccade. At the 100 ms sampling rate, the device would not be able to isolate many of the small eye movements, including the regressive saccade movements which are amongst the primary characteristics of the dyslexic eye movement pattern.
U.S. Pat. No. 4,003,642 teaches the use of a linear data array to facilitate the digital processing of the output of an eye movement detector.
U.S. Pat. No. 4,474,186 discloses a computerized electro oculographic system with a feedback control for the stimuli This patent teaches the use of a computer to analyze the output of an EOG detector and to alter the stimulus administered to the observer in accordance with previously analyzed test results. The analysis performed on the eye movement data, however, is not at all similar to the analysis conducted by applicant's invention. In addition, at the present time, an EOG system is not sensitive enough to reliably detect small eye movements.
U.S. Pat. Nos. 3,842,822 and 3,952,728 to Levinson, et al. disclose various types of dismetric dyslexia screening devices or procedures. Neither of these references, however, analyze the eye movement of the subject.
U.S. Pat. No. 4,102,564 discloses the analysis of eye movements for detecting a neurological condition, particularly nystagmus, which consists of spontaneous oscillatory short and jerky movements of the eyes.
U.S. Pat. No. 4,368,959 discloses an apparatus for and method of testing vision which alters the visual stimulus in order to test for and detect the presence of multiple sclerosis.
U.S. Pat. No. 4,237,383 entitled "High Speed Loading of Output Register of CCD Array System" discloses a semi-conductor array used in an imaging system which has a charge and read cycle sufficiently high to be used as part of an eye movement detector intended for use in the present invention.